Glass products have long been made from a pre-formulated feedstock (also sometimes termed a glass batch) that is charged into a glass furnace and melted to produce molten glass for subsequent formation into the desired glass product. A typical feedstock includes a physical mixture of virgin raw materials and, optionally, recycled glass materials known in the industry as “cullet.” The virgin raw materials contain quartz sand (crystalline SiO2) and other ingredients, such as soda ash (Na2CO3) and limestone (CaCO3) for soda-lime-silica glass, for example, and the cullet primarily contains shards of glass from previously-formed consumer or commercial glass products. The cullet component of the feedstock can vary based on the glass-forming process being practiced and the desired characteristics of the final glass product (e.g., color, transparency, etc). In many instances, however, the feedstock may contain up to about 80 weight percent cullet, with the remainder being virgin raw materials which may or may not include, in addition to the ingredients listed above, a small percentage of other ingredients including glass network formers, network modifiers, colorants, decolorants, fining agents, and redox agents, to name but a few.
The residence time of the conventional glass feedstock in the glass furnace is relatively long. This can be attributed to several factors. First, the largest component of the virgin raw materials, quartz sand, and usually some of the other virgin raw material ingredients—e.g., soda ash and limestone for soda-lime-silica glass—are crystalline materials. Their crystal structures, including intermediate crystalline phases, are generally present up to about 1200° C., as melting and dissolution of these materials does not occur instantaneously. Second, the glass feedstock needs to be dispersed and homogeneously mixed by convection after being melted to produce molten glass, which is a time-consuming process. Quartz sand, in particular, takes the longest to disperse on account of its slow dissolution rate and the tendency to agglomerate into SiO2-rich regions within the glass melt known as “cord.” The presence of cord is indicative of glass inhomogeneity and may result in imperfections or defects in the finished glass product. Third, some of the virgin raw material ingredients—e.g., soda ash and limestone for soda-lime-silica glass—are carbonate-containing materials that, when melted, release carbon dioxide (CO2). The evolution of carbon dioxide during feedstock melting introduces bubbles in the resultant molten glass, which, in turn, can cause a thin spot or bubble defect in the finished glass product. Any such bubbles are typically removed from the molten glass in a process known as “refining the glass.” To address the challenges associated with melting and homogenizing crystalline raw materials and to remove bubbles caused by carbon dioxide evolution, among other factors, conventional glass feedstocks are usually subjected to high temperatures and heating times of 24 hours or more in the glass furnace in order to obtain suitably-refined and chemically homogenized molten glass.
The melting of the glass feedstock can be made less taxing if some of the virgin raw materials are replaced with cullet in the feedstock. The cullet accelerates the melting of the feedstock and lowers furnace energy consumption as compared to a feedstock that contains all virgin raw materials. Cullet has this effect because it has already been melted, mixed, and formed into a glass product and will not release carbon dioxide when re-melted since it is not an intrinsic carbonate-containing material. But cullet is not widely available as a commodity in some regions and, even if it is, bulk purchases of the recycled material are subject to great variations in color and other characteristics that may restrict glass manufacturing options. Post-consumer cullet also has the tendency to be contaminated with metals, glues, and other organics, and is sometimes difficult to uniformly mix with virgin raw materials in the glass furnace when melted. Moreover, even with the addition of cullet, current glass manufacturing practices still typically involve melting the glass feedstock and homogenizing/refining the molten glass in the glass furnace at a temperature of around 1400° C. or higher for at least about 24 hours. Such long processing times at elevated temperatures require a lot of energy and slow the overall glass-making process.
One or more embodiments set forth in the present disclosure may achieve any of a variety of objectives including, for example, obtaining a glass precursor gel that can be melted without requiring long residence times in the glass furnace in order to achieve homogeneous and refined molten glass. The glass precursor gel has a bulk amorphous oxide-based matrix that includes a homogeneous chemical mixture of the primary constituent oxides and any secondary materials, in the proportions desired, of the final glass product composition. Moreover, when the glass precursor gel is heated and melted, it releases no more than a negligible amount carbon dioxide due to the fact that it does not include carbonates. Because the glass precursor gel includes an already homogenous chemical mixture of the primary constituent oxides, as well as relatively small amounts of any other secondary materials, and because it does not contain carbonates, it does not require a lengthy refining process; rather, it only needs to be heated for a relatively short period of time to obtain a homogeneous and bubble-free molten glass that is ready for downstream production into a glass product.
The present disclosure embodies a number of aspects that can be implemented separately from or in combination with each other.
In accordance with one aspect of the present disclosure, there is provided a glass precursor gel that comprises a bulk amorphous oxide-based matrix. The amorphous oxide-based matrix is homogeneously chemically mixed and includes 30 mol % to 90 mol % silica and at least one of the following: (A) 0.1 mol % to 25 mol % of one or more alkali oxides (mol % is the sum total), (B) 0.1 mol % to 25 mol % of one or more alkaline earth oxides (mol % is the sum total), (C) 1 mol % to 20 mol % boric oxide (B2O3), (D) 5 mol % to 80 mol % lead oxide (PbO), or (E) 0.1 mol % to 10 mol % aluminum oxide (Al2O3). The glass precursor gel has a density of less than 2.0 g/cm3.
In accordance with another aspect of the disclosure, there is provided a method of making a glass product. The method includes obtaining a glass precursor gel that comprises a homogeneously chemically mixed bulk amorphous oxide-based matrix and an extending swelling agent. The bulk amorphous oxide-based matrix has an inorganic network of primary constituent oxides. The primary constituent oxides comprise 30 mol % to 90 mol % silica and one or more of the following: (A) 0.1 mol % to 25 mol % of one or more alkali oxides (mol % is the sum total), (B) 0.1 mol % to 25 mol % of one or more alkaline earth oxides, (C) 1 mol % to 20 mol % boric oxide, (D) 5 mol % to 80 mol % lead oxide, or (E) 0.1 mol % to 10 mol % aluminum oxide. The method further includes melting the glass precursor gel into molten glass and forming the molten glass into a glass product.
In accordance with yet another aspect of the disclosure, there is provided a method of making a glass product. The method involves providing a silicate solution that includes a dissolved sodium silicate comprising a molar ratio of Na2O:SiO2. A soluble calcium salt is added to the silicate solution to displace some of the sodium oxide in the dissolved sodium silicate with calcium oxide and to derive a wet precipitate that comprises a molar ratio of Na2O:CaO:SiO2. Solvent is then removed from the wet precipitate to obtain a soda-lime-silica glass precursor gel that comprises a homogeneously chemically mixed bulk amorphous oxide-based matrix having an inorganic network of 60 mol % to 85 mol % silica, 8 mol % to 18 mol % sodium oxide, and 5 mol % to 15 mol % calcium oxide. The soda-lime-silica glass precursor gel is melted into molten glass which, in turn, is formed into a glass product.